The present invention relates to particular ethylene copolymers having relatively uniform crystallinity and residual unsaturation, and formed by the copolymerization of ethylene and 1,3 butadiene (diolefin) comonomer in the presence of a metallocene/aluminoxane (alumoxane) catalyst. According to the present invention ethylene-butadiene copolymers are obtained having high molecular weight, a lower degree of crystallinity than the high ethylene content ethylene-butadiene co-polymers of the prior art, and a relatively high degree of unsaturation. The ethylene-butadiene copolymers of the invention are characterized by improved clarity, toughness and lower unsaturation than ethylene butadiene copolymers of the prior art.
The present invention is concerned with unsaturated, crystalline copolymers comprising macromolecular polymer chains made up of copolymerized units of ethylene and butadiene in which the butadiene is incorporated on the backbone in the form of trans 1,2 cyclopentane. It is well known that 1,3 butadiene and ethylene may be co-polymerized with a conventional Ziegler catalyst to form the unsaturated 1,4 (cis and trans) and the unsaturated 1,2 configurations (vinyl branch on the chain backbone). The object of the present invention is to provide new, unsaturated copolymers of ethylene and 1,3 butadiene in which a portion of the diolefinic comonomer is incorporated as a bulky, saturated cyclic unit. In these new copolymers, a portion of the units derived from the 1,3 butadiene exist in the copolymer in the form of cyclopentane units, and the remainder of the units derived from the 1,3 butadiene exist in the form of the 1,4 (cis and trans) and 1,2 configurations, the unsaturation being retained.
Additionally, prior art ethylene copolymers are generally characterized by relatively inefficient use of comonomer moieties along the polyethylene chains. The distribution of the comonomer along the chain is very important in determining both the efficiency of use of the comonomer and the resulting properties of the polymer, especially with respect to crystallizability of the polymer. The prior art ethylene copolymers tend to have a high degree of clustering or contiguity of the comonomer moieties along the polyethylene chain. That is, the comonomer units are adjacent or clustered along the chain resulting in inefficient use of the comonomer since only a single polyethylene chain crystallinity interruption results between adjacent polyethylene chains when several comonomer units are contiguous and clustered together. This has important implications in the total amount of comonomer required to achieve a certain level of crystallinity that is, in the case of inefficient use more comonomer is required to achieve a desired crystallinity. Also, it is often disadvantageous and costly to require unneeded portions of comonomer, especially when dealing with less available and more expensive diene comonomers such as 1,3-butadiene. Additionally, the need to use a higher portion of comonomer also tends to force the comonomer into low molecular weight, high comonomer content ends of the molecular weight distribution.
As indicated, the ethylene-1,3-butadiene copolymers of the present invention are highly unsaturated curable elastomeric hydrocarbon copolymers. These copolymers are not only outstanding elastomers in their own right, but they are valuable intermediates for the preparation of adhesives, sealants and the like and yield useful products as components in blends. To enhance these useful features of the instant ethylene-1,3-butadiene copolymers, it has been found desirable to achieve relatively homogeneous distribution of the unsaturated diene comonomer across the polyethylene copolymer chains.
It has now been found that new 1,3-butadieneethylene copolymers can be prepared by co-polymerizing ethylene and 1,3 butadiene in the presence of metallocene/alumoxane catalysts. The copolymers are found to be unsaturated and possess certain broadened molecular weight as well as comonomer sequencing and distribution characteristics.